1. Technical Field
The present disclosure relates to a heat storage apparatus and a method of completing crystallization of a heat storage material.
2. Description of the Related Art
A heat storage material is a material that can store hot heat or cold heat. The hot heat or the cold heat stored in the heat storage material is dissipated as demanded. A heat storage material that is capable of storing hot heat or cold heat primarily by making use of exothermic reaction or endothermic reaction occurring due to a phase change of a substance is called a latent heat storage material. In this specification, a latent heat storage material that is capable of storing cold heat and dissipating the cold heat as demanded may be called a latent heat cold storage material or simply a cold storage material.
Among latent heat cold storage materials, a latent heat cold storage material having a high thermal storage density that allows a hydrate called a clathrate hydrate to be formed by cooling, such as a tetrabutylammonium bromide (TBAB) aqueous solution and a tetrahydrofuran (THF) aqueous solution, is available. Even if such a latent heat cold storage material is cooled to a hydrate generation temperature or less, the latent heat cold storage material tends to be in a supercooled state. Therefore, it is difficult to stably use such a latent heat cold storage material as a cold storage material. Consequently, a technology of cancelling the supercooling of such a latent heat cold storage material is proposed.
For example, Japanese Unexamined Patent Application Publication No. 2015-187535 (Patent Literature (PTL) 1) describes a supercooling preventing apparatus that uses a tetrabutylammonium bromide (TBAB) aqueous solution as a cold storage material. The supercooling preventing apparatus includes a first cold-storage-material storing unit, a voltage applier, a second cold-storage-material storing unit, and a cooler. The first cold-storage-material storing unit stores a cold storage material. The second cold-storage-material storing unit is connected to the first cold-storage-material storing unit, and stores cold storage material. The cooler cools the cold storage material in the second cold-storage-material storing unit to a hydrate generation temperature or less. The voltage applier applies a voltage to the cold storage material in a state in which the temperature of the cold storage material in the first cold-storage-material storing unit is less than the hydrate generation temperature.
Japanese Unexamined Patent Application Publication No. 2010-133688 (Patent Literature (PTL) 2) describes a supercooling releasing method of releasing a supercooled state of a heat storage material. In this method, a contact portion where at least a portion of a first member and at least a portion of a second member whose coefficient of thermal expansion differs from that of the first member normally contact each other without being joined to each other is provided in the heat storage material. In this method, relative sliding between the first member and the second member at the contact portion, caused by a difference between the coefficient of thermal expansion of the first member and the coefficient of thermal expansion of the second member, is considered an opportunity to release the supercooled state of the heat storage material. For example, according to this method, it is confirmed that the supercooled state is canceled within one hour when a TBAB aqueous solution is used as a heat storage material.